The problem can be corrected by upgrading the affected package to version 2:0.92-1ubuntu04.10.1. In general, a standard system upgrade is sufficient to effect the necessary changes.

Details follow:

USN-157-1 fixed some vulnerabilities in the Mozilla Thunderbird email client. The updated Thunderbird version broke compatibility with the Enigmail plugin. As announced in USN-157-1, the Enigmail package was now updated for Ubuntu 4.10 (Warty Warthog) to work with the new Thunderbird version.